Investigate the key features of stellar spectra and describe how these are used to classify stars

Investigate the key features of stellar spectra and describe how these are used to classify stars

  • Stars are divided into seven spectral classes based on their surface temperatures: O, B, A, F, G, K and M.
  • This system of classification was developed by Annie Jump Cannon.
    • O is the hottest class.
    • M is the coolest class
Spectral classSurface temperature / KColourSpectral Features
O28,000 – 50,000BlueIonised helium lines Strong UV component
B10,000-28,000BlueNeutral helium lines
A7500-10,000Blue-whiteStrong hydrogen lines Ionised metal lines
F6000 − 7500WhiteStrong metal lines Weak hydrogen lines
G5000 − 6000YellowIonised calcium lines Metal lines present
K3500 − 5000OrangeNeutral metals dominate Strong molecular lines
M2500 − 3500RedMolecular lines dominate Strong neutral metals

*Metal refers to any element apart from Hydrogen and Helium

  • Each class is divided into ten further subdivisions using the numbers from 0 to 9.
  • Our sun is a G2 star.
  • The hotter a star is, the shorter its dominant wavelength is.
  • Thus, by observing wavelengths through spectroscopy, temperature can be determined and stars can be classified.

 

Extract from Physics Stage 6 Syllabus © 2017 NSW Education Standards Authority (NESA)